Updates available, but no install option since dcpromo on 2008 ser

Hi, I've been trying to resolve this for ages. We have 4 2008 servers (fresh
build) that recevied their updates successfully from our WSUS server (hosted
on a 2003 WSUS server). We then ran dcpromo on the 4 2008 servers to make
them domain controllers. Since then if you log onto the 2008 DC's (even as
the domain 'administrator') the notification pops up on the ask bar to say
'New updates are available', but when I open the 'Windows Update' window I
have no 'Install Updates' option.

We've since build other 2008 servers and they all work fine, as long as they
are not DC's.

So how do I get my 2008 DCs to give me the 'Install Update' button? Any help
would be much appeciated.